Wound Healing Lab Research

Adhesive Agents

One type of agent that is currently being researched extensively in our laboratory, and in conjunction with the Tissue Adhesive Center, is fibrin sealant. Fibrin sealant is composed primarily of fibrinogen and thrombin, compounds naturally found in our blood. Altering the concentrations, or strengths, of either the fibrinogen or the thrombin changes the properties of the sealant and allows it to be used in a variety of ways to achieve three surgical goals. For instance, a very quick-setting sealant can be used to stop tissues from bleeding or to seal off tissues from their surroundings. A slower set allows the user to apply the sealant to two surfaces and then approximate the tissues to effectively glue the surfaces together.

Our laboratory has devised several models with which to test the strength and efficacy of various fibrin sealant formulations as used to achieve each of the three surgical goals listed above: hemostasis (stopping of bleeding), tissue sealing, and tissue gluing.

More information about fibrin sealants can be found in the following reference:
WD Spotnitz et al. The role of sutures and fibrin sealant in wound healing, Surgical Clinics of North America,
77(3), 651-669, 1997.

Bone Void Fillers

Missing Content

Skin Equivalents

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Surgical Adhesions

Adhesions as a complication of surgery continue to be a cause of significant morbidity despite several years of basic science and clinical research. Many different injury models have been used in various laboratory animals, leading to difficulty extrapolating results from one model to another.

The focus of our research has been to create uniform, reproducible models of adhesion formation and then quantify the strength of the resulting adhesion. By using injury models that generate nearly 100% adhesion, the efficacy of experimental adhesion prevention agents be properly and accurately evaluated. Our laboratory has currently extended its range of models to include abdominal adhesions, flexor tendon adhesions, gynecological adhesions, and, most recently, spinal adhesions following laminectomy. Further information about our model of abdominal adhesions can be obtained from the following reference:
ES Harris et al. Analysis of the kinetics of peritoneal adhesion formation in the rat and evaluation of potential antiadhesive agents, Surgery 117(6):663-669, 1995.

Surgical Suture & Needle Mechanics

Suture Mechanics: Surgical sutures continue to be changed and improved as new synthetic materials and new manufacturing processes become available. Our laboratory has established reproducible tests to document improvements in strength, handling, and other important clinical characteristics. For instance, strength can be tested both out-of-package to measure maximum strength, and at certain appropriate time points after implantation into tissue. The latter test is especially important for absorbable sutures. Such strength retention information is valuable when determining what type of suture to use in a given tissue. Suture handling characteristics such as ease of repositioning a two-throw knot, suture drag through tissue, and knot security (how many throws of a square knot need to be tied to ensure that the knot breaks when pulled rather than slipping undone) provide quantitative data about the qualitative notion of handling.

Needle Mechanics: Several parameters important to the successful performance of surgical suture needles have been identified in our laboratory and needle tests are performed on an ongoing basis. The three main parameters are: sharpness, resistance to bending, and ductility (or resistance to breakage). The needle of choice will be sharp, to ensure that it elicits minimal trauma in its passage through tissue; strong enough to resist bending, for weak needles that bend during use lead to uncontrolled trajectories and increased trauma to the tissue; and ductile, so as to minimize the chance of breakage during use. Needle sharpness is determined by measuring the maximum force required to push the needle tip through a thin, uniform, synthetic membrane. Resistance to bending is determined by rotating each needle against an adapter fitted to a load cell. The bending forces generated are converted to bending moments. Needles that withstand larger bending moments before becoming permanently bent are the more preferable. The design of the needle ductility test is similar to that of the bending test. The needle is rotated against the load cell adapter through 90 degrees of rotation. The needle is then rotated back to its original position. This cycle of rotation is repeated until the needle breaks. The work required to cause needle breakage can be calculated after converting bending forces to moments.

A more detailed description of our testing of sutures and needles can be found in the following two references:
GT Rodeheaver et al. Biomechanical and clinical performance of a new synthetic monofilament absorbable suture, J. Long-Term Effects Med Implants, 6(3&4): 181-198, 1996.

WL McClung et al. Biomechanical performance of ophthalmic surgical needles, Ophthalmology, 99(2): 232-237, 1992.

Wound Irrigation

Cleansing contaminated soft-tissue wounds to rid them of inflammatory stimulants is an indispensable part of the effective wound care protocol. Irrigation must be performed effectively yet with a minimum of physical and chemical trauma. Because these goals are at odds with each other, a balance must be reached. Research has been undertaken in our laboratory to determine how to achieve that balance.

Physical trauma occurs when the pressure exerted on the wounded soft tissue exceeds the tissue's capacity to absorb it. Studies in our laboratory have shown that impact pressures (pressues actually delivered to the tissue) of 4-15 pounds per square inch (psi) are effective in removing a substantial amount of contaminants from the wound while keeping penetration of the tissue by the stream to less than 15% of the tissue thickness. In contrast, irrigation streams pressurized to 20 psi penetrate the full thickness of the tissue without removing significantly more contaminants from the surface.

Chemical trauma must also be minimized. We have focused on the cytotoxicity (the cell-killing ability) of various commercially available skin and wound cleasers by assessing white blood cell viability and functionality after exposure to these cleansers. Skin cleansers and wound cleansers with added antiseptic agents were more toxic to cells than were non-antiseptic wound cleansers. For further reading on wound irrigation, see:

TB Hellewell et al. A cytotoxicity evaluation of antimicrobial and non-antimicrobial wound cleansers, Wounds, 9(1),
14-19, 1997.

PA Foresman et al.: A relative toxicity index for wound cleansers, Wounds 5(5), 226-231, 1993.

N Bergstrom, J Cuddigan, ed. Treating Pressure Ulcers. Guideline Technical Report, No. 15, vol. 1. Rockville, MD: U.S. Dept. of Health and Human Services, Public Health Service, Agency for Health Care Policy and Research. AHCPR Publication No. 96-N014. Dec. 1994.